1. Field of the Invention
This invention relates broadly to containers for handling solutions which must be maintained essentially free of microbial growth and to methods of preserving such containers and solutions. More particularly, the invention relates to ophthalmic dispensers and preserved ophthalmic solutions.
2. Description of the Related Art
Various contact lens care solutions for improving consumer comfort and safety are currently being marketed. Examples include wetting solutions to enhance the lens compatibility with the eye; storage solutions which prevent lens dehydration, microbial contamination, or optical distortion; and cleaning solutions which remove lipids, proteins, or other biological matter attached to the lens surface. In addition, there are numerous ophthalmic solutions designed to reduce ocular discomfort, treat ocular illnesses, or enhance ocular wound healing (e.g., subsequent to surgery). Many of these lens care solutions and ophthalmic treatment solutions, both referred to herein as ophthalmic solutions, are provided to the consumer in plastic containers or aerosol cans having a nozzle or tip through which the solution is dispensed.
Many ophthalmic solutions are dispensed directly into the eye of the consumer, and the tip of the dispenser may contact ocular tissue or fluids. Thus, microbes or ocular pathogens may contaminate the ophthalmic dispenser, and over extended storage times, may increase to concentrations which may threaten the consumer's health or comfort when the ophthalmic solution is introduced into the eye. Solution contamination may also occur by merely exposing the solution to the surrounding air, which exposure may occur when a consumer dispenses the solution. Accordingly, ophthalmic solutions typically include a preservative or antimicrobial, such as polymyxin B sulfate, quaternary ammonium compounds, chlorobutanol, organic mercurials, p-hydroxybenzoic acid esters, certain phenols or substituted alcohols.
A different type of preservative is required in solutions which include an active agent or drug which is unstable under certain conditions. For example, pilocarpine is known to be unstable at basic pH levels. In order to prevent degradation of the active agent, preservatives may be added to the solution. In the case of pilocarpine, preservative acids or buffers may be added to prevent degradation.
The use of such preservatives in ophthalmic solutions is problematic because the preservatives may cause irritation when they contact ocular tissues. For example, benzalkonium chloride (BAK) is known to be a useful ophthalmic preservative, and has broad antibacterial and antifungal activity in combination with other additives, such as disodium ethylene diaminetetraacetic acid (EDTA). However, BAK may denature corneal protein, causing eye damage and discomfort. Further, some consumers have allergic reactions to some preservatives, such as BAK, even at relatively low concentrations.
U.S. Pat. Nos. 5,056,689 and 5,080,800, both issued on application of Heyl, et al., disclose a remarkably innovative solution to the aforementioned ophthalmic preservative problem. These patents teach the use of a "scavenger" material in the tip of the ophthalmic dispenser. As the solution is dispensed through the scavenger-containing tip, the preservative is removed from the solution. Depending on the preservative used, the scavenger may "remove" preservative by a chemical reaction which neutralizes the preservative, by ion exchange, by adsorption, by absorption, and the like. Thus, the solution which is dispensed from the tip into the consumer's eye is virtually preservative-free, thereby avoiding or minimizing any of the previously described problems associated with the preservative's contacting ocular tissue. Advantageously, the ophthalmic solution within the container remains microbe-free, because preservative within the solution inhibits microbial growth.
However, a problem which may arise with the Heyl, et al. invention is that the scavenger media itself may not be sufficiently preserved. While preservative inhibits microbial growth in the ophthalmic solution within the container, the preservative has been removed from the scavenger media and any ophthalmic solution remaining on the scavenger media. Thus, microbes contaminating the tip media may be allowed to propagate, thereby increasing concentrations to unacceptable levels.
Hence, there is a need for a method of preserving scavenger media within the tip of an ophthalmic dispenser, without causing introduction of unacceptable levels of preservative into the eye during dispensing. Analogously, there is a need for an ophthalmic dispenser having a scavenger tip which is itself preserved.